Method of producing water vapor permeable sheet material

ABSTRACT

Coagulation process and apparatus for producing thick microporous polyurethane sheet material by passing a sheet of polymer extended with liquid vehicle beneath a close spaced plate with liquid non-solvent fed to the gap between the plate and the surface to produce controlled imitation of the coagulation.

United States Patent Warwicker 1 1 Apr. 24, 1973 [54] METHOD OFPRODUCING WATER 3,073,733 1/1963 Mitchell ..264/218 X V P PERMEABLESHEET 3,100,721 8/1963 Holden ..264/41 UX MATERIAL 3,190,765 6/1965 Yuan..264/41 UX 3,238,055 3/1966 Brightwell ..264/41 UX [75] Inventor: EricAibert Warwicker, Kings Lynn, England FOREIGN PATENTS OR APPLICATIONS[73] Assignee: Porvair Limited, Norfolk, England 22 FiledZ June 2 1970284,725 7/1928 Great Britain ..264/218 [21] App]. No.1 42,793 PrimaryExaminerPhi1ip E. Anderson Att0rneyAbner Sheffer [52] U.S.CI. .264/41,117/132 B, 117/132 C,

117/1388 F,161/159,161/190,161/D1G.2, [57] ABSTRACT 264/216, 264/D1G.62, 264/D1G. 77 I 51 Int. Cl ..B29d 7/22, B29d 27/04 Coagulauo" Processand apparatus for Producmg [58 Field of Search ..264/41 49 216 thickmicroporoS Polyurethane Sheet material by 264/217, 218, 178 R, 2 3" DIG.62 DIG. passing a sheet of polymer extended with liquid vehi- 161/159190 G 2; 15 /305 cle beneath a close spaced plate with liquid non-s01-vent fed to the gap between the plate and the surface [56] ReferencesCited to produce controlled imitation of the coagulation.

UNITED STATES PATENTS 16 Claims, 4 Drawing Figures 1119,329 9/1934Weingand ..264/218 X LAYER 0F COAGULA TING LIQUID OSUPPOORT EELT51 LAYERor TOPCOAT PASTE LAYER or SUBSTRATE PASTE Patented April 24, 19733,729,536

2 Sheets-Sheet 2 70 l l I l l l l l L l 70 2U 4U 5U 7U 8U 700 INVENTOREmc A. WARWIQLEQ mmgg b AT TO R NE METHOD OF PRODUCING WATER VAPORPERMEABLE SHEET MATERIAL The present invention relates to methods ofmaking microporous polymer materials particularly but not exclusivelymaterials free from preformed fibrous sheet reinforcement and toapparatus for carrying out the method.

The invention is concerned with microporous polymer materials which areproduced by coagulating layers of polymers extended with liquidvehicles, for example, polymer solutions, gels or colloidal dispersionswith liquid non solvents. It has been suggested that the non-solvent canbe applied to the surface of the layer of polymer solutions as a vapor,but this is not feasible for relatively thick layers, e.g., 0.5millimeters upwards, or as a spray but this produces an uneven surface.The more usual method is to pass the layer on a support with the supportuppermost into a bath of the liquid non-solvent.

This presents considerable problems in conveying the material throughthe bath especially in a continuous process since the polymer layer mayrequire a substantial period of time, e.g., of the order of one-halfhour before the polymer surface can be conveyed around a roller withouta surface blemish being produced.

The applicants have observed that attempting to pass the layer on asupport with the layer uppermost into a bath of liquid non-solventbrings a number of problems. Thus the passage of the material into thebath of liquid and plant vibrations tend to set up ripples in thesurface of the bath and these can often cause surface patterns whichhave an adverse effect on the appearance of the material and render itunsuitable for use as high grade man-made leather-like material.

Thus an object of the present invention is to provide a process adaptedto continuous operation to produce a material of consistently goodappearance.

A further object of the present invention is the provision of a compactand simple plant for carrying out the said process.

The present invention finds a particular application in the productionof relatively thick polymer layers free from preformed fibrous sheetreinforcement for example from 0.5 millimeters up to as thick as 5millimeters or more and especially to the production of layers having athickness making them suitable for use as shoe upper materials forexample 0.8 millimeters to 1.5 millimeters preferably 0.8 to 1.1millimeters for womens weight shoes and 1.1 to 2.5 millimeterspreferably 1.5 to 1.8 millimeters for mens weight shoes.

In order to produce such materials in vapor permeable or microporousform from a layer on a support of solutions of polymers for examplepolyurethanes, in organic hygroscopic or hydrophilic solvents, forexample N,N dimethylformamide, the said solutions containing microscopicwater soluble particles, for example ground sodium chloride, bycoagulation with liquid non-solvents for example water or water solventblends, the layer when immersed support uppermost in the aqueoussolution needs to remain immersed for about one-half to 1 hour toachieve coagulation of the polymer to self supporting form when thefinished layers are to be about 1.5 to 2 millimeters thick. Longerperiods are required for thicker layers and vice versa.

At speeds of entry into the non-solvent through an unstabilized surfacewith the polymer sheet uppermost or less than 10 to 15 feet per minutesurface patterns due to ripples are very likely to occur on the surfaceof the coagulated polymer layer. Until the material has been immersed innon-solvent for at least one-half hour, it cannot be conveyed around aroller without the material being damaged. The present invention enableslow speeds for example 1 to 3, 5 or 10 feet per minute to be usedresulting in shorter production lines and substantial savings in spaceand cheaper plant.

The applicants have discovered that many of these problems can beovercome if the layer of polymer extended with liquid vehicle isarranged uppermost on a support and liquid non solvent in continuousform applied thereto. This is carried out at least for long enough tocoagulate the immediate surface. The remainder of the coagulation can becarried out in the same or similar way even by spraying or by immersionin the conventional manner.

The applicants have also discovered that this application of non-solventcan be particularly conveniently carried out if a layer of polymersolution on a support is passed through a gap or slot and the gap orslot is sufficiently narrow for a stabilized meniscus to be set upbetween the upper surface of the layer and the adjacent wall of the slotwhen liquid non-solvent is supplied therebetween. The surface of thematerial can be coagulated in this way with a smooth surface and thecoagulation can be completed thereafter either by continued treatmentwith a thin layer of non-solvent held smoothly against the coagulatedsurface as by overlying spaced plates or trailing flexible sheets, or byimmersion of the layer in a conventional bath of non-solvent.

Moreover this enables the layer to be coagulated whilst supporteduppermost on a support, the support can thus easily be conveyed throughthe process and the conveying problems and the requirement for largetanks of non-solvent associated with upside down coagulation can beavoided.

The present invention also enables much smaller volumes of non-solventto be used for the coagulation and attendant removal of the bulk of theliquid vehicle or solvent. This reduces the scale of operation neededfor solvent recovery, allows the composition of the non-solvent liquidto be more readily controlled, and makes it possible should it bedesired for a wide range of non-solvents such as alcohols glycols,ketones and other non-solvent liquids other than pure water to be usedincluding these containing dissolved solids having non solvent actionsuch as inorganic salts for example ammonium compounds such as ammoniumnitrate. The smaller volumes required both reduce the capital cost ofthe non solvent and fire risks and other hazards.

Whilst the process and apparatus is particularly suited to theproduction of unreinforced microporous polymer layers its advantageswill also be obtained in the production of reinforced layers. Thus whena sheet of polymer extended with liquid vehicle or polymer extended withliquid vehicle in sheet form is referred to both unreinforced andreinforced polymer compositions are included within the term unlessotherwise stated. Thus the invention is applicable to the coagulation ofpolymer extended with liquid vehicle not only when the polymercomposition exists as a single homogeneous layer but also when it existsas a number of superposed layers of varying compositions for examplevarying in polymer, pigment, stabilizer or other component nature orcontent, as also when the polymer composition forms a coating on or isimpregnated into reinforcing sheets for example of woven, non woven orknitted fibrous material and especially needle punched polymerimpregnated felts such as described in British Pat. specification Nos.9147] l and 914713.

Thus according to one aspect of the present invention a method of makinga water vapor permeable, preferably microporous, polymer sheet materialcomprises at least initiating the coagulation of polymer extended withliquid vehicle in sheet form, preferably arranged uppermost on asupport, by applying liquid nonsolvent in continuous form to at leastone surface of the said sheet, desirably by forming a continuous,desirably thin, layer of liquid non-solvent extending across the widthof the sheet on the said surface of the said sheet, preferably by movingthe said sheet past means for forming the said layer. Preferably theapplication of non-solvent is carried on at least long enough tocoagulate the immediate surface of the layer, i.e., so that a surfaceskin is formed and the layer is no longer sticky to the touch.

The liquid non-solvent is applied by means which are held out of contactor do not come into contact with the free surface of the polymer layer.Thus the surface remains flat and smooth and does not conform to theprofile of the means which apply the liquid non-solvent, i.e., thesemeans do not exert pressure on the surface of the layer such as toconform or modify the configuration of the surface.

According to another aspect of the invention a method of making a watervapor permeable preferably microporous polymer sheet material comprisescoagulating at least one surface of a sheet comprising polymer extendedwith liquid vehicle by causing continuous relative movement of the saidsheet with respect to a body of coagulating liquid, a surface of thesaid sheet coming into contact with the said body of coagulating liquidalong a line of contact bounding an exposed surface of the said body ofliquid while the said liquid surface is stabilized along a line spacedfrom the said surface of the sheet not more than 1 centimeter andpreferably in the range 0.1 to 8 millimeters especially 2 to 7millimeters.

Preferably the said liquid surface is stabilized by the presence of asolid boundary located along the said spaced line. Desirably thedistance between this said boundary and the surface of the sheet is suchas to enable a meniscus of non-solvent liquid to form thcrebetweenv Thedistance between the solid boundary and the surface of the said sheet isdesirably maintained substantially constant during the relative movementwhich conveniently consists of the sheet being moved past the bodyofliquid.

Reference has been to the relative movement being continuous."l'he useof this term is not intended to mean that the movement persistsindefinitely but merely is carried out for substantial periods of time,e.g., numbers of hours or days rather than minutes and more importantlythat it is not intermittent and is of substantially constant speedduring a given period of operation of the process. Clearly, however, thespeed can vary from run to run depending on the relevant factorsinvolved in the particular run.

The continuous layer of liquid non-solvent can be formed by a variety ofmeans though a preferred form of apparatus utilizing a close spacedplate and the surface tension of the non-solvent is described below.

In the preferred form of the invention the body of liquid can beconsidered as a layer located between the plate and the sheet. However,the exact length of this layer of non-solvent in the direction ofrelative movement of the sheet and the means forming the layer ofnon-solvent, the machine direction, can vary though in the preferredembodiment this first layer is some 15 to 30 cms (6 to 12 inches) long.

This body of liquid may constitute a layer but should have a definedlinear upstream boundary preferably stabilized at least againstmacroscopic movement so that any movements in the non-solventsubsequently in contact with the sheet are substantially prevented fromreaching the said upstream boundary where the coagulation commences.

Whilst the plate and slot arrangement described below is found toproduce very satisfactory results and is preferred the body of liquid orlayer may not need to extend any finite length in the machine directionso long as a defined thin linear region of non-solvent is established.Thus a bar extending across the sheet in close spaced relationship couldbe used as could be a porous pipe similarly spaced and fed with liquidnon solvent or a spaced calendar roll rotating with the same surfacespeed as the sheet in the same direction.

Also the non solvent could be fed evenly onto the surface from a slitextending across the sheet which would be inclined so that the liquidwould flow in the same direction as the sheet was moving. Thenon-solvent could also be thickened with suitable thickening agents andextruded onto the sheet, the thickening agents being removedsubsequently in the coagulation.

However the specific embodiments described hereafter are preferred tothese alternatives.

It has been mentioned above that the continuous layer of non-solventused to initiate coagulation is desirably thin and that it is preferredthat the coagulation is completed by maintaining a substantiallycontinuous and again desirably thin layer of non-solvent on at least thefree surface.

The thickness of the layer of non solvent is not thought to be criticaland can be as thin as desired in order, for example, to reduce thevolume of liquid from which the solvent will have to be recoveredprovided that it is adequate to meet the sheets requirements to achieveeven coagulation as rapidly as possible.

Thus the layer does not need to be thicker than 1 centimeter thick andcan be as thin as 0.1 millimeter though at this thickness it may becomedifficult to maintain the layer in substantially continuous form. Auseful and readily achieved thickness for the non-solvent layer is inthe range 1 to 5 millimeters particularly when water containing up to10% w/w of dimethylformamide is used as the non-solvent. A wetting agentmay usefully be added to the non-solvent to assist in the maintenance ofthe layer of non-solvent.

Another advantage of the use of a thin layer of non solvent rather thana bath of non solvent is that the concentration of liquid vehicle orsolvent in the non solvent more rapidly reaches a level at which solventrecovery is economically feasible and thus the non-solvent need be usedfor shorter periods of time and can be kept more pure, than is the casewhen baths of nonsolvent are used, with attendant plant and processadvantages.

The support may be made of any material which is sufficiently flexibleto run through the process and has sufficient solvent and temperatureresistance to withstand the process conditions and also is such that thepolymer layer adheres to its surface at least sufficiently to produce aflat layer on the surface of the support.

The support can thus comprise woven, knitted or non-woven textilematerials, flexible polymer sheet materials and flexible metal materialssuch as wire gauze. The textile materials are preferably made frompolyester fibers though any other solvent resistant fiber could be used.

When woven supports having a regular array of holes are used the supportpreferably has the following characteristics. The support preferably hasa stiffness (as herein defined) in the transverse or weft direction inexcess of (S5 1) 0.6 and (5%) 0.9 preferably 0.8 and 1.3 and especially1.8 and 2.2 whilst being flexible in the longitudinal direction, asupport area (as herein defined) in excess of 50 percent, preferably 60percent and especially 70 to 95 percent and at least 500 passages persquare inch, preferably 1,000 and especially 5,000 to 10,000, providingcommunication from face to face of the support.

Stiffness is measured using the three point beam loading method. Thespan of the sample between the two knife supports is 3.8 centimeters andthe load rate used is millimeters per minute and is applied downwardlyto the center of the sample. Stiffness (8%) is defined as the load inKgs required to produce a A centimeter deflection and stiffness (8%) isdefined as the load in Kgs. required to produce a 5: centimeterdeflection.

Support area is defined as the percent of the total area of the surfaceof the support which is occupied by the material of the support and iswithin 0.5 millimeters of the surface. With woven fabrics there may beprimary and secondary support areas and the sum of these is the supportarea as defined herein. Primary support is the area provided by the warpthreads (and possibly also weft in a plain weave) at the highest pointsin the surface and is the percent of the total area provided by suchthreads above a plane passing through their mid points at the highestpoints in the surface. Secondary support is the percent of the totalarea less the primary support provided by all threads above a planepassing through the mid points of the weft threads at their point ofnearest approach to the surface.

Thus in general terms primary support except in plain weaves is providedby the warp threads and secondary support by the weft threads. In plainweaves weft and warp both contribute and there is no secondary support.

The support can be porous or non-porous but if it is non-porous thesurface is preferably treated as by roughening it to produce a surfacekey for the polymer layer. Whilst the process is applicable to theproduction of permanent coatings on supports, it finds particularapplication in the production of unsupported sheet materials and in thiscase the support must be one from which the coagulated polymer layer canreadily be stripped without being damaged.

This stripping stage may result in a desirable drawing out of the innersurface of the material imparting a smooth fibrous appearance to ithaving in certain cases marked resemblance to the flesh surface of aleather produced from a natural hide, thus obviating the need for a shoelining when the articles are used as shoe uppers.

One particular material, which is both self supporting and has a degreeof flexibility and gives a very good flesh surface appearance, is aporous liquid permeable sintered polymeric plastics material especiallyone made from high density polyethylene and preferably having an averagepore size of 50 microns or more broadly 25 to 100 microns as measured bythe method described in B.S.S. 1752;1963 using n propyl alcohol. Such amaterial is sold under the name VYON (Trade Mark).

Preferably the support at least at its edges is such as to provide a keyfor the polymer sheet such that the force required to remove the sheetfrom the keyed area is below the breaking strength of theself-supporting sheet at the time at which the sheet is removed from thesupport, but in the range 50 to 2,000/grams per centimeter width,especially 90 to 1,400 grams per centimeter width.

The sheet can be removed immediately after coagulation or after beingleached when a filler is used or after being dried.

The degree of adhesion can be controlled by wetting the support beforethe layer is formed on it either with solvent or liquid vehicle or withnon-solvent liquids either pure non-solvent or non-solvent/solventblends having non-solvent action. Thus the support desirably is treatedso as to have an even non-solvent content prior to the applicationthereto of the sheet of polymer extended with liquid vehicle so as toensure even penetration of the support and that any coagulation causedby the non-solvent content of the belt is also even. The support maythus carry an amount of nonsolvent liquid prior to the application ofthe layer of polymer to it so as to ensure that in conjunction with thesurface properties of the support the layer of polymer adheres to thesupport without curling away from it but is still capable of beingstripped from the support without rupturing once the polymer has beencoagulated to self-supporting form.

The support preferably carried 50 to percent by weight based on its ownweight of the non-solvent liquid. The non-solvent liquid may comprise 5to 40 percent of the liquid vehicle the balance being the liquidnon-solvent.

Reference has been made to the polymer layer on the support being passedthrough a surface of liquid nonsolvent which surface is stabilizedagainst movement. The word through is not to be taken as excluding thecase where the surface of the polymer layer forms one boundary of thestabilized surface and indeed this is the most convenient way ofcarrying the invention into practice.

Thus, according to a further aspect of the invention a method of makinga water vapor permeable polymer sheet material comprises forming aninitial mixture comprising polymer extended with liquid vehicle, forminga layer of the initial mixture on a support passing the layer on thesupport past coagulating means for establishing a thin continuous layerof non solvent across the polymer layer with a stabilized upsteamboundary and establishing such a layer of non-solvent on the surface ofthe said polymer layer. As mentioned above the invention also extends toapparatus for carrying out the process of the invention.

Thus according to this aspect of the invention apparatus for coagulatingpolymer extended with a liquid vehicle in sheet form on a support whichmay be porous or non-porous comprises first means for evenly applyingliquid non-solvent in continuous form across the full width of the saidsheet at least to the free surface of the said sheet irrespective of theorientation of the said sheet on the support, and drive means arrangedto move the said sheet on the support past the said coagulating means.Preferably the support is arranged to have the sheet on its uppersurface and the coagulating means are arranged to establish a continuouslayer of liquid non-solvent across the full width of the sheet.Desirably the coagulating means are such that the upstream boundary ofthe layer of liquid non-solvent is substantially stabilized againstmovement. Thus the coagulating or first means may utilize the surfacetension of the liquid non-solvent to stabilize its upstream boundary.

Thus the apparatus desirably includes coagulating means for establishinga thin continuous layer of liquid non-solvent across a surface whilstthe said surface passes the coagulating means, the said thin layer ofliquid having a stabilized upstream boundary in the sense of movement ofthe said surface, means for forming a layer of an initial mixture on asupport the surface of the layer remote from the said support comprisingthe said surface, and means for passing the layer on the support pastthe said coagulating means so that the said layer of liquid non-solventis established'and the said surface of the initial mixture iscoagulated.

The first or coagulating means may comprise a plate positioned inclose-spaced relationship to the free surface of the sheet so as to forma slot therebetween and means for supplying non-solvent so as to keepthe slot filled. The thickness of the slot is desirably such that whennon-solvent is supplied to the downstream end of the plate the surfacetension of the liquid establishes a meniscus, adjacent to the upstreamend of the plate,

between the plate and the free surface of the sheet on the support.

The coagulating means preferably comprise a strip or plate arrangedtransverse to the direction of travel of the support and adjustablyspaced from the surface of the support so that a slot can be producedsuch as to enable a meniscus to be set up in the gap between the stripor plate and the surface of the polymer layer remote from the support. Afurther plate is preferably arranged beneath the support. Thenon-solvent supply means preferably comprise porous tubes extendingacross the width of the plate. These are preferably placed above thedownstream end of the plate.

They are conveniently made of the sintered high density polyethyleneVYON (Trade Mark) material described above. The production of this typeof material is described in British Pat. specification Nos. 750,239 and953,359 the disclosures of which are incorporated herein by reference.

They have the advantage of filtering the non-solvent supply andproviding an even feed and are cheap and can thus be easily replaced.

As mentioned above in a preferred form of this aspect of the inventionthe thin layer of non-solvent is maintained on the surface of the layerof polymer on the support until the said layer of polymer issubstantially completely coagulated to self-supporting form.

This is preferably achieved by arranging the support to run over anelongated tray with spaced plates or sheets arranged over the supportand a non-solvent supply arranged to maintain the said thin layer ofnonsolvent in the gap between the said plates or sheets and the saidsurface of the polymer layer. The sheets may be freely floating on thelayer of non-solvent and may be merely secured at their upstream end.

The non-solvent may be provided at a number of stations spaced down thetray with drain slots across the tray prior to the next inlet station.The arrangement can then run on a countercurrent basis by feeding theoutflow from each stage to the inlet of the preceding upstream stage.This arrangement enables a controlled concentration gradient of solventand non-solvent to be set up, and controlled at any desired level.

This enables the procedures disclosed in British Pat. specification No.981,642 to be readily carried out. However, whilst these may bedesirable for certain systems of polymer extended with liquid vehicle asdisclosed in that document they are not essential to the satisfactorycoagulation of the polymer-removable filler-solvent pastes preferred foruse in the present invention.

The plate may be at a slight angle to the horizontal so that the supportpasses downwardly beneath the plate, the angle being such that themeniscus can be established merely by supplying non-s0lvent on to thepolymer surface adjacent to the downstream edge of v the plate.

Preferably means are provided to maintain the free surface of the saidsheet at least wetted with non-solvent until the polymer issubstantially completely coagulated.

These means may comprise at least one covering sheet positioned abovethe polymer layer downstream of the plate so as to establish andmaintain a thin film of non-solvent evenly over the surface of thepolymer layer.

The method and means by which the layerof nonsolvent is maintained canbe varied. Thus fine sprays or mists could be used to keep the surfacewet but care would.have to be taken to ensure that the wetting was evenacross the full width of the layer and for its full length until fullycoagulated.

In another form of the invention the apparatus comprises meanscontaining a body of liquid non-solvent, means for introducing the sheeton the support into the body of liquid non-solvent at a substantialangle to the horizontal, plate means arranged to extend above thesurface of the body of liquid non-solvent so as to produce a slotbetween the free surface of the polymer sheet on the support and theplate, the slot being of such dimensions that in conjunction with theheight of the plate above the still surface of the body of liquidnon-solvent any ripples which are produced in the body of liquid as bythe passage of the support into it are dampened out at the meniscusproduced adjacent to the top of the plate between the free surface ofthe polymer sheet and the plate. 1

In a preferred'form of the invention means are provided to maintain boththe free surface of the said sheet and the free surface of the saidsupport at least wetted with non solvent until the polymer issubstantially completely coagulated.

The polymer is preferably dissolved in solvent but the term polymerextended with liquid vehicle is intended to cover systems in which thepolymer is in emulsion, colloidal or gel conditions as well as those inwhich it can reasonably be described as being in solution. Suchcolloidal or gel conditions are conveniently achieved by addition ofnon-solvent to a polymer solution. Examples of this method are disclosedin British Pat. specification Nos. 914,711, 946,069 and 984,088.However, any method, such as addition of an electrolyte, as disclosed inBritish Pat. specification No. 1,126,060, which reduces the solubilityof the polymer in the solvent can be used to achieve a colloidal or gelcondition.

The disclosures of these four specifications are incorporated herein byreference.

The non-solvent is preferably removed, as by drying, subsequent to theremoval of the solvent, it merely being necessary that, whilst anysolvent remains such as could cause disadvantageous reduction inpermeability sufficient non-solvent remains to prevent this happeningfor example by using a non-solvent with a higher boiling point than thesolvent.

If the viscosity of the system is insufficient to enable sufficientlythick coatings to be formed it can be increased by cooling the mixtureor adding thickening agents or by other conventional means.

A high vapor permeability was mentioned above as being desirable in shoeuppers for certain uses. Whilst a degree of porosity can occur when alayer of a polymer solution is bathed with a non-solvent for the polymermiscible with the solvent, the pores formed whilst imparting some vaporpermeability are liable to be not predictably or evenly distributed andmay vary widely in size depending on a wide range of parameters.

An even fine pore size can be ensured by distributing evenly through thepolymer solution finely divided particles of a removable filler, forexample a solid powder of an inorganic salt, which remain solid in thepolymer solution or are arranged to be in a finely divided solid statewhilst the polymer is coagulated and are removed at that time orthereafter for example by a leaching agent.

Preferably the ratio in parts by weight of removable filler to workingmaterial in the initial mixture is in the range 1.5 to l up to 3.0 to 1preferably about 1.7 to 1 up r2 to 1 and the ratio in parts by weight ofworking material to solvent in the initial mixture is in the range 20:80to 40:60, for example 25:75 to 35:65. Preferably the filler is ground sothat more than 50 percent of the particles have diameters in the range 4to 20 microns.

It will be appreciated that the variation of the parameters of polymerconcentration and removable filler concentration for a given polymerconcentration, i.e., filler to polymer ratio will affect the propertiesof the article, an increase in filler to polymer ratio and a decrease inpolymer concentration tending to produce a more open, i.e., morepermeable structure. A balance can conveniently be struck between thesetrends as discussed in the present applicants co-pending British Pat.application Nos. 1612/67 (Case PP.26) and 1608/67 (Case PP.27), thedisclosures of which are incorporated herein by reference.

Thus, if it is wished to produce a strong essentially microporousmaterial with essentially no macropores visible to the unaided eye, forexample using a thermoplastic essentially linear polyurethane derivedfrom a polyester by reaction with a diol and a slight excess ofdiisocyanate dissolved in dimethylformamide and using sodium chloride asthe removable filler and water as the leaching agent, then the polymerconcentration is desirably in the range 25 to 35% w/w, especially about30% w/w and the filler to working material ratio is preferably in therange 1.5 to l to 2.0 to l in parts by weight.

If it is wished to produce a more open and plump material having asubstantial number of macropores which result in softer more resilientmaterial then using the same system the filler polymer ratio is selectedto be about 0.5 to l.

lt will be appreciated that the leaching agent for the filler does notneed to be the same as that for the solvent, thus for example when thesolvent is dimethylformamide, it could be removed by methanol and thefiller for example sodium chloride could be removed with water.

The polymer can be any organic resin material which is capable offorming a film on coagulation from an emulsion, a colloidal dispersion,a gel or a solution, whether the film is water vapor permeable or not.

The polymer must also be capable of undergoing the various processesspecified in the methods described below. However, when the product isintended for use .as a man-made leather-like material an elastomericpolymer is preferably used. The particular strength and wearcharacteristics required for the end use of the man-made leather-likematerial will determine the particular polymer to be used.

For shoe uppers high abrasion resistance and tear strength combined witha reasonable extensibility and initial modulus to provide proper wearcomfort on the foot are required.

Many thermoplastic polymers can be used, for example polyvinylchlorideand its copolymers, acrylonitrile polymers and copolymers andpolyurethanes or blends of one or more of these.

The elastomeric polyurethane may be used on its own or as blends withminor proportions say up to 49 percent preferably less than 20 percentof polyvinyl chloride and other polymers and copolymers such as nitrilerubbers including solid copolymers of butadiene and acrylonitrile.

Other polymers which have been suggested for use in man-madeleather-like materials include polyacetal resins, vinyl halide polymers(including copolymers with other ethylenically unsaturated monomers),polyamides, polyesteramides, polyesters, polyvinyl butyral,polyalphamethylstyrene, polyvinylidene chloride,

polymers of alkyl esters of acrylic and methacrylic acids,chlorosulphonated polyethylene, copolymers of butadiene andacrylonitrile, cellulose esters and ethers, polystyrene and otherpolymers made from monomers containing vinyl groups.

The preferred polymers however are elastomeric polyurethanes havingrecovery properties intermediate between pure rubbers and purethermoplastic materials at room temperature.

The article by Schollenberger Scott and Moore in Rubber Chemistry andTechnology VoLXXXV, No.3, 1962, pages 742 to 752 at page 743 and in FIG.3 indicates the long so-called half lives of the polyester urethanesmade from adipic acid, 1,4 butane diol and diphenyl methane p,pdiisocyanate by the methods disclosed in U.S. Pat. No. 2,871,218 andsold under the Trade Mark ESTANE 5740. These two disclosures areincorporated herein by reference.

Polyurethanes may be based on a wide variety of precursors which may bereacted with a wide variety of polyols and polyamines andpolyisocyanates. As is well known the particular properties of theresulting polyurethanes to a large extent can be tailored by suitablechoice of the reactants, reaction sequence and reaction conditions.

The preferred polymers are elastomeric polyurethanes based on a linear,hydroxyl terminated polyester (although a polyether or apolyether/polyester blend may be used) and a diisocyanate, with a smalladdition of a difunctional low molecular weight reactant. The lastmentioned component may be added either with the other reactants at thestart of a one-step polymerization or at a later stage when it will actprimarily as a chain extender.

This type of polyurethane having thermoplastic properties isparticularly preferred for use in producing shoe uppers. Particularlypreferred polyurethanes are those derived from polyesters by reactionwith diols and diisocyanates. As is known from U.S. Pat. No. 2,871,218,mentioned above, many different polyesters, diols and diisocyanates canbe used, but a particularly suitable polyurethane system is one in whicha polyester made from ethylene glycol and adipic acid is reacted with1,4-butylene glycol and with 4,4- diphenyl methane diisocyanate.

In the system in accordance with the above specification the mole ratioof polyester and diol can vary between quite wide limits but thecombined mole ratio of polyester and diol is arranged to be essentiallyequivalent to the mole ratio of diisocyanate so that the resultantpolymer is essentially free of unreacted hydroxyl or isocyanate groups.

Polymers of this type but having an improved Shore hardness can be madeby using a slight excess of diisocyanate and also by using a copolyesteras by replacing part of the ethylene glycol in the above system by 1,4-butylene glycol.

A further alternative polyurethane system which has been foundparticularly suitable uses polyesters derived from caprolactones. Suchpolyurethanes are described in British Pat. specification No. 859,640,the disclosure of which is incorporated hereby by reference.

The polymers may be produced by a bulk polymerization process andsubsequently dissolved in suitable solvents or may be prepared directlyin solution by a solution polymerization process.

Polyurethanes made in solution as described hereafter are particularlypreferred. An improved form of that type of polyurethane isdisclosed inU.S. Pat. application Ser. No. 819,337. The disclosure of thatspecification is incorporated herein by reference.

The polymer can include conventional stabilizers, fillers, processingaids, pigments, dyes, additives and surface active agents for exampleproofing or wetting agents.

Any material which is essentially insoluble in the solvent for thepolymer and is inert to the solvent and the polymer but which is solubleor can be rendered soluble by a liquid which has no deleterious effectson the polymer can be used as the removable filler. However, inorganicsalts such as ammonium sulphate and particularly sodium chloride arepreferred because of their ready availability and the ease with whichthey can be converted to a finely divided form. The use of suchtemporary fillers has the added advantage that the mixture containingsuch fillers has a substantially higher viscosity than the polymersolution or polymer extended with liquid vehicle and this facilitatesthe form ation of thick layers. Whilst the preferred method ofcoagulating the polymer is to wash it or immerse it in a liquidnon-solvent for example water or water solvent blends for example of upto 40 percent or more dimethylformamide concentration any other liquidcoagulating method can be used which deposits a continuous though waterpermeable layer. Such other methods include using a liquid non-solventcontaining high concentrations of dissolved electrolytes, for example 15percent or higher aqueous sodium chloride solution. The removable fillermaterial is preferably microscopic particulate material which preferablycan be removed by dissolution or thermal decomposition. In place of ortogether with, the salt particles, other poreforming microscopicparticulate material may be used. These particulate materials may bestarch particles (which may be removed by treating the coagulated layerwith an aqueous starch-digesting agent, such as an enzyme, of knowntype). Or they may be other microscopic solid particles which areinsoluble in the polyurethane solution at least at the stage when thepolymer is coagulated, for example urea, and which can either bydissolved out by treating the coagulated sheet with water or othersuitable solvent for the particles which is a non-solvent for thepolyurethane or can be otherwise destroyed or removed; examples of suchparticles are sodium carbonate, oxalic acid, ammonium carbonate, orsuitable microballoons. Alternatively the void-forming particulatematerial may be in the form of dispersed microscopic droplets of aliquid insoluble in the solution of polyurethane or in the form ofdispersed microscopic bubbles of gas.

Additionally the pore formation could be controlled by dispersingremovable or permanent fibrous fillers such as polyvinyl alcohol fibersor polyamide fibers or by incorporating permanent particulate fillers,such as silica, preferably a very small particle size for example lessthan 1 micron.

When a removable filler, such as sodium chloride, is used the pore sizeof the resultant water vapor permeable material depends to some extenton the particle size of the removable filler in the paste and if amicroporous material is to be made then none of the filler particlesmust be larger than microns, and preferably most are substantiallysmaller, for example less than 50 microns typically in the range 1 to 40or 3 to 20 microns.

Many solvents are known for organic polymers and any suitable one can bechosen for the particular polymer used and preferably an organic solventis used. However, for elastomeric polyurethanes, N.N'-dimethylformamide, dimethyl sulphoxide, N-methyl pyrrolidone,dimethylacetamide and tetrahydrofuran are particularly useful.Dimethylformamide, dimethyl sulphoxide and the other solvents can bediluted with other cheaper solvents such as toluene andmethylethylketone which although not solvents for polyurethanes on theirown do not act as non-solvents when mixed with dimethylformamide or theother solvents mentioned above.

The invention may be put into practice in various ways and two specificembodiments will be described by way of example with reference to theaccompanying diagrammatic drawings.

FIG. 1 shows a longitudinal cross section schematic diagram of apparatusin accordance with the invention,

FIG. 2 shows a longitudinal cross section of a simple continuous processembodiment of apparatus in accordance with the present invention, and

FIG. 3 shows a longitudinal cross section, enlarged, ofa portion of FIG.1,

FIG. 4 is a stress strain curve for the polymer contained in solution S1described below in connection with Example 1.

THE APPARATUS SHOWN IN FIG. 1

This consists of an endless conveyor belt 51 of woven polyester fabric 3feet wide passing around an idler roller 52 and a driven roller 53 in aclockwise direction.

The dry belt is about 1.5 millimeters thick, weighs 107 grams per squarefoot and is made from polyester multifilament fiber (TERYLENE TradeMark) in a close woven twill weave. It has a 0.2 percent stretch atpounds pull per inch width 1.2 percent stretch at 50 pounds and 6.6percent stretch at 100 pounds. Its breaking point is at 327 pounds atwhich stage the stretch 21.7 percent.

These results were measured using an Instron tensile testing machine at1,000 percent extension per minute as described below. The belt is athick dense but flexible material.

The upper part of the belt runs through a gently inclined tray 54 about40 feet long. At the upper end of the tray the belt passes through aslot 55 formed between parallel glass plates 56 and 57. The lower plate57 is about 2% feet long and the upper plate 56 is about 6 inches longand is adjustably mounted so that the thickness of the slot 55 can bevaried 16. A spray 60 or tap connected to a supply of water or otherliquid nonsolvent is positioned just downstream from the upper plate 56.Four cross bars 61 carrying trailing polyethylene sheets 62 about 6 feetlong are positioned evenly across the tray the first one startingimmediately below the spray 60. A tank 63 to receive the liquid flowingoff the end of the tray 54 is positioned below the roller 53. Theapparatus also comprises a reactor vessel for preparing polyurethane insolution and pipework, storage tanks pumps and mixing apparatus fordistributing microscopic salt particles, stabilizers and otherprocessing aids evenly through the polymer solution to produce one ormore pastes and then delivering the pastes to one or more extrusion dieslocated adjacent to the upper end of the tray 54.

The apparatus shown in FIG. 1 is provided with two 30 inches wideso-called coathanger extrusion heads 66 and 67 so that a single ordouble layer of paste can be formed on the belt as desired. The rate offeed of the paste to the heads is adjusted to give the required wetcoating thickness for example in the range 0.1 millimeters to 3.0millimeters for each layer, e.g., 0.1 or 0.5 to 1.0 for the the toplayer and 0.7 or 1.2 to 1.8 or 2.5 for the substrate layer. The head 66will be referred to as the substrate head and the head 67 will bereferred to as the topcoat head.

The apparatus is used as follows. A polyurethane is formed in solutionin dimethylformamide from a polyester by reaction with a diol anddiisocyanate under an inert atmosphere as described in more detail inExample 1. The polyurethane solution containing approximately 30 percentby weight of resin solids is mixed with microscopic sodium chlorideparticles about 2 (e.g., or in the range 1.0 to 2.5) parts by weight perpart by weight of resin and with small amounts of stabilizers andpigment. This substrate paste is evenly mixed and deaired and fed to thedie 66 to produce a layer of about 0.070 inches (1.8 mm) wet thicknesson the belt 54. A top coat paste is formed in similar manner butcontains 3 (e.g., in the range 2.5 to 5 or 6)parts of sodium chlorideper part of resin and is fed to the die 67 to produce a layer of about0.030 inches (0.76 mm) wet thickness on top of the substrate layer. Thebelt contains 50 to 80 percent preferably about percent non-solventliquid, e.g., water, by weight just prior to the first head 66. Thecomposition of this liquid is usually predominantly water but it maycontain from say 5 to 40 percent by weight of dimethylformamide andpreferably 10 to 20 percent by weight. The layers on the belt are thenpassed at 1 foot per minute through the slot 55. Water at 5 to 60C inthis case about 15C is supplied to the spray 60 at a rate sufficient tomaintain the gap between the top surface of the paste layers and theunderside of the plate 56 filled with liquid. This gap is arranged to beabout 1 to 3 millimeters, in this case one-sixteenth inch or 1.6millimeters thick so that a stable meniscus is set up at the upper endof the slot and a smooth coagulated surface produced. In the steadystate this liquid is observed by sampling at the center of the slot tocontain about 5 percent by weight of N,N-dimethylformamide. The watersupply is sufficient to maintain the slot full of water and alsomaintain a film of water over the whole surface of the paste layers forthe full length of the tray.

In this arrangement the belt is stopped after 35 feet of paste have beenspread on the belt and the belt held on the tray with the water supplymaintained for at least 70 minutes to complete the coagulation of thepolymer to microporous self-supporting form. The wet self-supportingsheet is then stripped from the belt and immersed for 2 hours in waterat 60C to reduce the chloride ion content to 1,000 milligrams per squaremeter or less thus removing substantially all the salt and substantiallyall the dimethylformamide. The material is then dried at 98C.

THE METHOD FOR USE WITH THE APPARATUS OF FIG. 1

The polyurethane polymers used were made in solution indimethylformamide from a polyester by reaction with a diol and adiisocyanate under an inert atmosphere.

The reaction was carried out in pure N,N'-dimethylformamide (139 BritishGallons) using 130 parts of an anhydrous adipic acid/ethyleneglycol/butane 1:4 diol copolyester having a molecular weight of about2,000 acid value less than 2 and a hydroxyl number of about 53, soldunder the Trade Mark DESMOPHEN 2001 (by Bayer) and 28.38 parts ofanhydrous butane 1:4 diol and 0.1022 parts of dibutyl tin dilaurate, 108parts of pure 4,4'diphenylmethane diisocyanate was then added and themixture cooled so as to keep the temperature below 50C. When thereaction was substantially complete additional butane 1:4 diol was addedto react with the remaining free isocyanate groups and the temperatureheld at about 50C until the viscosity was about 2,900 poise at 24C. Thisadditional diol was 2.2 parts. Finally 4.7 parts of a 1:1 methanol/NN-dimethylformamide blend was added to react with any traces of freeisocyanate still present. The viscosity at this stage of a sample at 24Cwas 3,900 poise, the solids content was 30 percent, the intrinsicviscosity was 1.04 and the Huggins slope constant k of the viscositynumber plot was 0.37. This solution will be referred to as solution S1.

A sample of solution S1 was then diluted to 15 percent resin solids andcast in a flat glass reservoir. The solvent was evaporated off slowlyover several hours and finally more rapidly under vacuum at 50C to givea substantially solvent free transparent film 0.2 millimeters thick.

The ultimate tensile strength was 544 Kg per square centimeter measuredby the method described in British Standard specification No. 3144/1958using an Instron tensile testing machine.

The notch tear strength was 128 Kg/centimeter.

FIG. 4 is a stress strain curve for this polymer film using a dumb-bellshaped sample as for ultimate tensile strength. The curve was arrived atby combining the load time graph from an Instron tensile testing machineon which the sample was extended at a constant rate of 50 percent perminute with an extension time graph plotted by hand using referencebench marks drawn on the sample to give the true strain. Both sets ofmeasurements were done at room temperature.

It can be seen from FIG. 4 that the initial modulus at 25 percentextension is 72 Kgs per square centimeter.

Table 1 gives the values of certain physical properties of other polymersolutions used in the examples.

The notch tear strength was measured on an Instron tensile testingmachine using the method described in British Standard specification No.2782:3/308A/ 1965 The specimen is cut with a single stroke of a pressusing a knife-edge punch with cutting edges of the form and dimensionsshown in FIG. 308,108 of the above British Standard.

The jaws of the testing machine are set 5 centimeters apart and the endsof the specimen gripped in the jaws. The jaws are then separated atcentimeters per minute and the load at which a tear is initiated at thenotch is recorded.

EXAMPLE 1 A stabilized topcoat polymer paste containing evenly dispersedmicroscopic salt particles was made by mixing 121.1 parts of polymersolution S9 with 35.4 parts of N,N'-dimethylformamide 126.4 parts offinely divided sodium chloride and 22.8 parts of a carbon black pigmentmaster batch.

The resultant paste contained 25 percent resin solids and had aviscosity of 87,000 centipoise at 25C measured on a BrookfieldViscometer.

The pigment master batch was made by dissolving in 32.2 parts ofN,N'-dimethylformamide 2.4 parts of STABAXOL a carbodiimide stabilizeragainst hydrolysis of the polyurethane, 3.2 parts of CYASORB U.V. 24,namely 2,2-dihydroxy-4-methoxy-benzophenone, a stabilizer against ultraviolet ray degradation of the polyurethane and 0.8 parts of IRGANOX1010, namely tetrakis [methylene 3-(3',5', ditertiary-butyl-4'-hydroxyphenyl propionate] methane, an antioxident for the polyurethane,and stirring into this 8.0 parts of Rajah Black carbon black pigmentand, then mixing in 38.8 parts of the polymer solution Sl describedabove.

The Rajah Black carbon black pigment is made by the channel process byColumbian International and is stated by them to have an averageparticle size of 0.02 microns, a surface area of 156 square meters pergram, an oil absorption to produce a fluid paste of l 1.3 millilitersper gram and to produce a stiff paste of 1.23 milliliters per gram, acarbon content of 95.2 percent, and a voltatile matter content of 4.8percent.

The sodium chloride was ground in a pin and disc mill with airclassification to separate out fines and return oversize particles forregrinding. The sodium chloride powder before dispersing in the polymersolution typically had an average particle size of the order of 10 to 20microns usually about 13 to '17 microns with a standard deviation of theorder of i 10 microns. This measurement wasmade by sedimentationmeasurements using a Photoextinction Sedimentometer manufactured byEvans Electro-Selenium Ltd., Model No.

TABLE I Ultimate Initial Viscosity Huggin's Resin tensile Notch tourmodulus poise at Intrinsic slope solids, strength, strength, (25%),Solution number 25 C. viscosity constant percent kgJcmfl kg./cm. kg/cm.

3, 900 I. 04 0. 37 30 544 128 72 1, 000 32 046 02 2, 300 32 534 144 622, 260 32 3, 040 32. 3 15K (11 1,500 31. a

41 used in accordance with the manufacturers instructions based onpapers by H.E.Rose in Engineering of Mar. 31 and Apr. 14, 1950, andNature of 1952, Volume 169, page 287.

This apparatus consists of a chamber in which the solid whose particlesize is to be measured can be dispersed ultrasonically in a liquid andits rate of settling measured optically. The change in transmission oflight by the dispersion with time is related to the particle sizes ofthe particles and the measurements of this change enable the averageparticle size to be calculated.

It will be appreciated that these sedimentometer experiments give anindication of the general order of particle size of the majority of theparticles.

Shadow photography of typical samples of the ground salt has indicatedthat the salt particles have random rough irregular shapes includingquite elongated shapes as well as more compact cube or block shapes.

The dispersions typically contain a few particles having a maximumdimension as large as 70 microns but substantially all of the particlesare less than 40 to 50 microns, and most are less than 25 to 30 micronsin maximum dimension and have dimensions in the range down to 1 micronor so though a few may be even smaller. The salt is also selected tohave a low moisture content so that it does not cake, for example lessthan 0.5 percent and especially in the range 0.2 0.4 percent. It mayalso have an anticaking agent added namely MlCROCAL at about 1 percentby weight. MICRO- CAL is a very fine particle size coprecipitated limeand silicate anticaking agent sold by Joseph Crosfield & Sons Ltd. Themixing and milling conditions are preferably carried out at relativehumidities less than 70 percent at 25C and preferably at about 50percent.

A substrate paste was made from a blend of solutions S1 and S2 and wasmixed with 1.78 parts per part of resin of microscopic sodium chlorideof particle size similar to that used in making the topcoat paste, and apigment master batch similar to that used for the topcoat paste so thatthe finished substrate paste contained 0.5 percent carbon black byweight based on resin.

The paste had a viscosity of 1,720 poise at 25C. The substrate andtopcoat pastes were then fed under pressure to the heads 66 and 67respectively at pump pressures of 62 pounds per square inch and 105pounds per square inch respectively with a belt speed of 1 foot perminute. The water supply to the spray 60 was mains water at C.

The material had the following physical properties thickness 1.65millimeters; weight 748 grams per square meter; ultimate tensilestrength L 11.0, X 11.8 Kgs. per centimeter, centimeter elongation atbreak L 300%, X 365%; initial modulus extension) L 3.2 Kg. percentimeter, X 2.8 Kg. per centimeter; notch tear strength L 5.3, X 4.8Kg. per centimeter; pore size 10.5 microns (maximum), 5.5 microns(average), hydrostatic head 106 millimeters of mercury and averagedensity (calculated) 0.45.

These physical properties were measured as described in Belgian Pat.specification No. 732,482.

EXAMPLES 2 TO 6 These were carried out in the same manner as Example lapart from the polymer solutions used and the fact that in Example 5distilled water instead of mains water was used as the non-solvent.Table 2 sets out the polymer solutions used, the viscosities of thepastes, the pump pressures to the extrusion heads, the belt speed andthe physical properties of the materials produced, and includes thevalues for Example 1 for comparison. The units used in Example 1 arealso used in the table.

TABLE 2 Example 1 2 3 4 5 6 Substrate paste Polymer S6/S5/ solutionS2/Sl S4 S7/S3 S7 S7 S7/S8 Paste viscosity 1720 1880 1360 1620 1620 1720Pump pressure psi 6 1 12 70 70 71 Topcoat paste Polymer solutions S9 S887/51 1/ 32/810 82/510 82/510 S12 Paste 870 1520 790 670 670 670viscosity Pump pressure psi 105 118 176 53 53 50 Belt speed 1 l 2 l l 1Product thickness 1.65 1.55 1.66 1.96 1.93 1.81 Weight 745 667 657 798756 753 UltimateL 11.0 9.3 9.2 11.0 10. 9.6 tensile strength X 11.8 8.88.1 11.7 11.3 10.6 Elongation L 300 278 313 318 309 291 at break X 365300 318 340 330 312 Initial L 3.2 2.7 2.3 3.1 3.0 3.0 Modulus X 2.3 2.62.2 3.2 3.1 3.3 25% extension Notch tear L 5.3 4.5 3.8 5.3 4.8 5.4strength X 4.8 4.4 4.1 5.5 5.4 5.4 Pore (av.) 5.5 5.1 5.1 size(max.)10.51l.1 10.3 Hydrostatic head 106 93 Water vapor permeability 4740 47404060 Average 0.45 0.43 0.40 0.41 0.39 0.42 density (calculated) Watervapor permeability was measured by the method described in BritishStandard specification No. 3177/1959, but at 37C and a nominal humiditygradient of percent relative humidity.

These materials are all flexible and have a handle and drape closelyresembling a high quality calf grain leather. They can easily be madewithout carbon black and post dyed or different pigments or dyes couldbe incorporated in the polymer pastes.

They can be given a variety of surface finishes to make them resemblenatural leather finishes for example they can be converted to suedes bybuffing or sanding and the surface which was in contact with the beltand carries an impression thereof can be rendered similar in appearanceto the flesh surface of natural leather by sanding. The surfaces canalso be embossed for example by using a patterned foil as disclosed inBritish Pat. specification No. 54377/67 (Case PP.33) the disclosure ofwhich is incorporated herein by reference.

A variety of surface modifying finishes can be applied to the top coator top surface of a single layer material for example to impart a grainleather like finish.

One very suitable finishing operation is a treatment of the uppersurface with fine droplets of a solvent and heating, in a manner topartially collapse the microporous structure along the surface and forma thin fused polyurethane skin thereon; materials so finished often havea series of tiny spaced depressions, partially lined with fusedpolyurethane material (e.g., about 2 to 15 microns in thickness), atsaid surface. Another suitable finishing treatment involves applying tothe upper surface of the microporous material a thin top coat, such asan aqueous emulsion of a suitable polymer (e.g., an alkyl acrylatepolymer or copolymer such as a copolymer of butylacrylate with some 15percent of acrylonitrile and about l-2 percent of itaconic acid, whichcan be cross-linked on heating by the inclusion of ureaformaldehydecondensation product in the emulsion, as is well known in the art); theamount of such polymer may be insufficient to close the pores, orsufficient to provide a very thin layer, less than about one micron inthickness, whereby the appearance of the material is improved withoutunduly decreasing its ability to transmit water vapor. The top coat maybe a continuous layer which imparts a glossy patent finish to thematerial; thus one may apply a conventional organic solvent solution ofpolyvinyl butyral mixed with solvent soluble melamine-formaldehyderesin, and evaporate off the solvent and cure (cross-link) the mixtureof these two resins.

The material could also be dyed with conventional dyes for polyurethanesfor example before the treatment with solvent spray or the applicationof the top coat or both.

In yet a further alternative form of coloring treatment a dye iscontained in the non-solvent in which the polymer is coagulated. The dyemay be an Irgacet dye as mentioned above and the non-solvent may be anaqueous alcoholic solution of the dye. Further details of the processand examples of other suitable dyes are disclosed in British Pat.Specification No. 20735/68 (PP.37) the disclosure of which isincorporated herein by reference.

These finished materials can be readily made into shoe uppers and thusinto shoes by conventional techniques.

THE APPARATUS SHOWN IN FIG. 2

This consists of an endless conveyor belt 10 of woven polyester fabricas described for FIG. 6 passing around three rollers 12, 13 and 14 andover an inclined tray 11. The tray III is arranged beneath the upperpart of the conveyor and supports it for a substantial part of itslength. The upper end 16 of the tray is on the same level as the top ofthe uppermost 14 of the three rollers thus providing a horizontal upperstretch of conveyor belt. The lower end 17 of the tray terminates justbefore the lower roller 12 and an end roller 13 is located at the samelevel as the roller 12 so that the lower part of the conveyor belt isheld in a horizontal plane. The rollers 12, 13 and 14 are arranged todrive the conveyor belt down the tray 11 around the end roller 12horizontally to and around the roller 13 up at a steep inclined angleand around the roller 14 and thence back to the top 16 of the tray 11.The lower part of the conveyor belt is arranged to be within a tank 20so that when liquid is placed in the tank the horizontal lower portionof the conveyor belt 10 will be beneath the surface of liquid. The tank20 also contains rollers 21 and 22 each placed respectively just beforethe rollers 12 and 13 in the direction of travel of the conveyor belt10. A guide roller 23 and a dancing roller are locatedoutside the tank20 together with a rewind reel 25 supported on rollers 26 and 27, roller26 being driven by a further roller 28.

A pair of calender rollers 30 and 31 are positioned between the rollers13 and 14 and are arranged to be capable of calendering the conveyorbelt to varying degrees.

A pair of extrusion heads 35 and 36 are located at the upper portion 15of the conveyor 10 so as to be adapted to lay down superimposed layersof polymer paste on the conveyor belt. At the top end of the tray 11 aplate 40 is supported adjustably parallel to the tray 11 so as toprovide a slot of adjustable thickness but of substantially greaterdimension in the direction of motion of the conveyor than its thickness.The plates extend across the full width of the conveyor. Immediatelydownstream of the plate in the direction of motion of the conveyor thereis arranged a Vyon tube 42 to feed liquid on to the surface of the plate40 at its downstream edge. Immediately downstream of this Vyon tubethere is a further glass plate about eight feet long provided with aVyon feed tube 44 adjacent its upstream edge. Bars and trailing sheets46 as in the arrangement shown in FIG. 1 are spaced down the rest of thetray. Below the end of each sheet 46 the tray has a transverse drainslot 47. Immediately prior to each bar 45 but downstream of thepreceding drain slot there is located an inlet pipe 48. The drainedliquid may either be discarded from the slots 47 or fed back to thepreceding inlet 48 acting in effect as a counter current.

Preferably pure water is fed in at the end of the tank 30 adjacent theroller 13 and the liquid fed in counter current from the end of the tankadjacent the roller 12 to the lower end of the tray 11. The water fedinto the tank is preferably at 40 to C and at the other end of the tankits temperature is about 30C and its N,N'- dimethylformamide contentabout 3 percent by weight. The outflow from the tank is fed to the tray11 in counter current and the final outflow 47 from the tray 11 isarranged to contain up to about 10 percent of dimethylformamide which isrecovered in a solvent recovery plant. The outflow could easily bearranged to have a higher solvent content but it has been observed thatas the solvent content increases in the initial coagulating liquid thecoagulated surface tends to be less smooth and can take on a mattappearance.

Measuring means (not shown) are located between the rollers 14 and theextrusion heads 35 between the two extrusion heads 35 and 36 and betweenthe extrusion head 36 and the plate 40 so as to enable control of thethickness of the extruded materials to be achieved. This can be done bymeasuring either the thickness or the weight of the material passing themeasuring means.

The equipment described above can be used to produce a water vaporpermeable self-supporting sheet material as follows:

The conveyor belt 10 is set running at the desired speed, e.g., l to 5or l0 preferably 3 to 5 feet per minute, the tank 20 is filled withliquid, for'example water, sprays 42 are supplied with liquid forexample water, and the pressure between the rollers 30 and 31 isadjusted to give the desired moisture content in the conveyor belt 10.The take-up drive roller 28 is synchronized with the speed of the belt10. The material which it is wished to coagulate comprising polymerdissolved or dispersed as a colloid or gel in a water miscible organicsolvent is fed to one or both of the extrusion heads 35 and 36 dependingon whether a single layer film or a double layer film is to be produced.The rate of feed of polymer to the heads is adjusted to give the desiredthickness or thicknesses, for example in the range 0.3 millimeters to3.0 millimeters. The film carried on the conveyor belt and adhering toit passes between the plate 40 and the tray 1 1. The separation of theplate 40 from the top surface of the extruded film is adjusted to besuch that a stable meniscus of liquid is established at the upper end ofthe plate 40. The film on the conveyor thus first comes into contactwith the coagulating liquid in a stabilized state and the surface isevenly coagulated. With water, even coagulation is produced when thismeniscus of one-fourth and preferably one-sixteenth inch or below inthickness. As the coagulating liquid is absorbed into the film furtherfresh liquid passes up beneath the plate 40 to replenish the meniscus.The film surface is thus rapidly coagulated and coagulation of the restof the layer or layers is continued as the conveyor passes beneath thesprays 42 and then under the further stabilized film of coagulatingliquid provided by the polyethylene sheet 44. This sheet minimizes theproduction of surface irregularities which are observed to occur when itis not used and the sprayed liquid is merely allowed to run down thesurface of the conveyor under gravity. The at least partially coagulatedfilm then passes round the roller 12 and beneath the surface of theliquid in the tank 20. It will be appreciated that the conveyor belt isnow uppermost and the film is underneath it. At the rate mentioned abovefor the conveyor and with the dunk tank 50 feet long the film takes 35minutes to pass from the roller 12 to the proximity of the roller 21.Within this time sufficient solvent has been displaced from the film forthe polymer to be in a self-supporting condition. The leading edge ofthe film can thus be detached from the conveyor and led round the roller21 and back through the tank for a further period of 35 minutes duringwhich a substantial proportion, if not all, of the solvent is displaced,depending on the thickness of the layer or layers. The film is then ledaround the roller 22 out of the tank over the roller 23 under thedancing roller 24 which controls the tension in the self-supportinglayer between the rollers 26 and 27 and then on to the reel in aclockwise direction under zero tension. The factors of film thickness,the nature of the solvent and coagulating liquid, the conveyor beltspeed and the temperature of the liquid in the tank 20 and the length ofthe tank 20 should preferably be selected to ensure that substantiallyall of the solvent is displaced from the polymer film but if outsidefactors make it desirable the process may be run so that some solventremains and this can easily be removed in a further treatment of theself-supporting sheet material with a solvent miscible non-solvent forthe polymer which may be the same as or different to the coagulatingliquid.-

The actual mixture fed to the extrusion heads could vary within widelimits but the apparatus is particularly suitable for use in conjunctionwith the formulations disclosed in British Pat. specification No.l,l22,804 and British Pat. specification No. 1608/67 (Case PP.27).

In an alternative form of the invention the tray 11 is dispensed with asis the roller 12 and they are replaced by roller arrangements whichdirect the conveyor belt into the liquid in the tank 20 at asubstantially vertical angle. The plate 40 is supported parallel to thedirection of entry of the belt into the tank and its upstream edge isarranged to be at a height greater than the maximum ripple heightencountered in the tank when running the apparatus. This once moreresults in a stable meniscus being established which is automaticallyreplenished by surface tension from the body of the liquid in the tank.The length of the plate is adjusted to damp down the motion of theripples so that the meniscus is held sufficiently stable for a surfacefree from dunk lines to be produced.

The function of calender rollers 30 and 31 mentioned above will now bedescribed in more detail.

Their function is to control the amount of coagulating liquid retainedin the belt when the process is running continuously. It is necessary todo this in order to achieve a balance between the need for sufficientadhesion of the polymer supplied from the extrusion heads to prevent thelayers distorting when coagulated and the conflicting need to strip theself-supporting film from the conveyor belt at the roller 21. If toomuch coagulating liquid remains in the belt 10 the adhesion of theextruded film will be insufficient and the shrinkage produced by theinitial coagulation of the top surface of the film at the plate 40 maybe such as to cause the edges of the film to separate from the conveyorbelt or delaminate. If too little coagulating liquid remained in thebelt, the adherence of the coagulated layer to the belt at the time itreaches the roller 21 could be too great and this could causedifficulties. Thus whilst the layer will be self-supporting at thisstage it will not yet have achieved the strength which it will haveafter further treatment and the stripping stage at the roller 21 mighteven cause damage to the layer.

The particular degree of moisture needed in the belt as it approachesthe extrusion heads will vary depending upon the factors mentioned abovein connection with the amount of solvent likely to remain in the belt atthe end of its passage through the apparatus but a balance can be struckbetween too great and too slight adhesion by trial and error.

According to a further aspect of the invention a method of making awater vapor permeable polymer sheet material which comprises coagulatingat least one surface of a layer of polymer extended with liquid vehicleon a support is characterized in that the method comprises causingcontinuous relative movement between the layer on the support and atleast two bodies of liquid non-solvent the sheet being transferred frombeing in contact with one body to being in contact with another by beinglead around guide means in a manner such that its free surface is heldout of contact with the said guide means and is prevented from assuminga concave transverse configuration.

Desirably the contact with the bodies of liquid non solvent is carriedon for sufficient time to coagulate not only the surface of the layerbut also to coagulate the layer to a form in which it can be strippedfrom the support.

The guide means preferably comprise a large diameter cylindrical orconvex guide surface such as a roll. By large diameter is meant asurface having a radius which is many times, e.g., to 50 or more timeslonger than the thickness of the layer on the support.

The layer is preferably also supported as by guides stentors or grips insuch a way as to prevent it assuming a convex transverse configurationat least during its contact with the first said body of liquid andpreferably throughout the period from its initial contact with the firstbody of liquid up to the stage at which it can be stripped from thesupport without rupturing.

The first body of liquid can be established in accordance with theaspect of the invention which uses a close spaced plate described aboveand this may be most convenient when only low speeds of operation, e.g.,up to 10 feet per minute are desired to be used. The second orsubsequent bodies of liquid can be established in the same manner.

Alternatively the second body of liquid can be provided by a tank, orbath such as is described with reference to FIG. 2.

Subsequent bodies of liquid if used could conveniently involve the trayand trailing sheet arrangements described with reference to FIG. 7 andwhilst the slot and plate entry arrangement might be a convenient way ofsealing the entry end of the tray to prevent nonsolvent spilling outother means such as idler rollers underneath the support or a smooth lipto the tray could be used.

Alternatively the first body of liquid can be provided by a tank or bathof liquid into which the layer on the support can be lead by beingpassed round guide means with the free surface of the paste away fromthe guide means so as to have the support uppermost in the tank.

As described above the support can then be held flat by stentors, gripsor other means.

The layer on the support would then pass out of the bath around furtherguide means and up and over a series of one or more trays as describedabove. The layer once coagulated could be stripped from the support.

The invention also extends to apparatus for coagulating polymer extendedwith liquid vehicle in sheet form on a support which may be porous ornon porous which comprises first means for applying a body of liquid nonsolvent at least to the free surface of the said sheet second means forapplying a separate body of liquid non solvent at least to the freesurface of the said sheet, drive means arranged to move the said sheeton the support past the said first and second means in sequence andguide means for transferring the sheet on the support from the firstmeans to the second means in a manner such that the free surface of thelayer is held out of contact with the said guide means and is preventedfrom assuming a concave transverse configuration.

What I claim as my invention and desire to secure by Letters Patent is:

1. In a method of making a water vapor permeable polymer sheet materialwhich comprises forming a layer at least 0.5 mm thick ofa polymercomposition in adherence with a support, the said polymer compositioncontaining a film-forming polymer and a solvent therefor and beingcoagulable to water vapor permeable self-supporting form by immersion inliquid nonsolvent for the polymer, said non-solvent being miscible withthe solvent of said polymer composition, and causing continuous relativemovement of the layer in adherence with the support with respect to abody of coagulating liquid which is a non-solvent for the said polymerand is miscible with said solvent, the improvement in which the freesurface of the said layer of polymer composition is brought into contactwith the said body of coagulating liquid along a line of contactbounding an exposed surface of the said body of coagulating liquid whilesaid exposed liquid surface is stabilized by the presence of a solidboundary which is in contact with said exposed surface of said body ofcoagulating liquid along a second line, said second line being within 1centimeter of the first mentioned line, whereby at least the said freesurface of said layer of polymer composition is coagulated to watervapor permeable form of improved surface smoothness.

2. A method as in claim 1 in which the said polymer compositioncomprising a solution of thermoplastic elastomeric polyurethane in aliquid selected from the group consisting of dimethyl formamide andblends of dimethyl formamide and water, microscopic particles of a watersoluble inorganic salt being dispersed through said polymer composition.

3. Process as in claim 1 in which the speed of said free surface of saidlayer of polymer composition with respect to said first mentioned lineis less than 15 feet per minute, and said layer of polymer compositionis maintained on the support until the layer is coagulated to selfsupporting form.

4. A method as claimed in claim 1 in which the distance between saidlines is maintained substantially constant during the relative movement.

5. Process as in claim 1 in which said layer of polymer composition isarranged uppermost on said support and there is a meniscus ofcoagulating liquid extending between said first and second lines.

6. Process as in claim 1 in which said support is porous, said solidboundary is stationary, said support carrying said layer is movedcontinuously, the speed of said support and layer of polymer compositionwith respect to said first mentioned line is less than 15 feet perminute, said body of coagulating liquid extends downstream (taken in thedirection of movement of said support and layer) of said solid boundary,and said layer and said support pass under said solid boundary.

7. Process as in claim 6 in which said speed is l to 10 feet per minute.

8. A method as claimed in claim 6 in which prior to the application ofthe layer of polymer composition to the porous support the poroussupport is dried and liquid non-solvent is evenly applied thereto so asto ensure even penetration of the support by the layer of polymercomposition and that the coagulation caused by the non-solvent contentof the belt is also even.

9. A method as claimed in claim 8 in which the support carries 50 topercent by weight based on its own weight of the non solvent liquid.

10. A method as claimed in claim 8 in which the nonsolvent liquidcomprises 5 to 40 percent by weight of the liquid vehicle the balancebeing liquid non-solvent.

11. Process as in claim 1 in which said porous support has an undersidewhich also contacts said body of 25 coagulating liquid, said polymercomposition and coagulating liquid being such that a microporous layeris produced by the process.

13. Process as in claim 12 in which the thickness of said thin layer ofliquid is l to mm and in which coagulating liquid is continuouslysupplied to said thin layer thereof.

14. Process as in claim 12 in which the width of said gap is in therange 0.1 to 8 mm.

15. Process as in claim 12 in which the width of said gap is in therange 2 to 7 mm.

16. A method of making a water vapor permeable polymer sheet materialwhich comprises forming an initial mixture comprising elastomericthermoplastic polyurethane dissolved in dimethylformamide withmicroscopic water soluble inorganic salt particles dispersed through themixture, forming a layer at least 0.5 mm thick of the initial mixture inadherence with a support, passing the layer in adherence with thesupport past a plate spaced from the free surface of the said layer adistance such that on supplying an aqueous non solvent liquid to the gapbetween the plate and the layer a meniscus is formed at the upstream endof the gap and supplying the said aqueous non-solvent for the polymer tothe said gap so as to establish and maintain the said meniscus of nonsolvent at the upstream end of the gap and coagulating said layer by theaction of aqueous non-solvent liquid thereon.

2. A method as in claim 1 in which the said polymer compositioncomprising a solution of thermoplastic elastomeric polyurethane in aliquid selected from the group consisting of dimethyl formamide andblends of dimethyl formamide and water, microscopic particles of a watersoluble inorganic salt being dispersed through said polymer composition.3. Process as in claim 1 in which the speed of said free surface of saidlayer of polymer composition with respect to said first mentioned lineis less than 15 feet per minute, and said layer of polymer compositionis maintained on the support until the layer is coagulated to selfsupporting form.
 4. A method as claimed in claim 1 in which the distancebetween said lines is maintained substantially constant during therelative movement.
 5. Process as in claim 1 in which said layer ofpolymer composition is arranged uppermost on said support and there is ameniscus of coagulating liquid extending between said first and secondlines.
 6. Process as in claim 1 in which said support is porous, saidsolid boundary is stationary, said support carrying said layer is movedcontinuously, the speed of said support and layer of polymer compositionwith respect to said first mentioned line is less than 15 feet perminute, said body of coagulating liquid extends downstream (taken in thedirection of movement of said support and layer) of said solid boundary,and said layer and said support pass under said solid boundary. 7.Process as in claim 6 in which said speed is 1 to 10 feet per minute. 8.A method as claimed in claim 6 in which prior to the application of thelayer of polymer composition to the porous support the porous support isdried and liquid non-solvent is evenly applied thereto so as to ensureeven penetration of the support by the layer of polymer composition andthat the coagulation caused by the non-solvent content of the belt isalso even.
 9. A method as claimed in claim 8 in which the supportcarries 50 to 80 percent by weight based on its own weight of the nonsolvent liquid.
 10. A method as claimed in claim 8 in which thenon-solvent liquid comprises 5 to 40 percent by weight of the liquidvehicle the balance being liquid non-solvent.
 11. Process as in claim 1in which said porous support has an underside which also contacts saidbody of coagulating liquid, said polymer composition and coagulatingliquid being such that a microporous layer is produced by the process.12. Process as in claim 6 in which said solid boundary is in suchrelationship to said layer of polymer composition that there is anelongated narrow gap between said layer and said boundary, which gap isfilled with coagulating liquid, and said coagulating liquid is sosupplied as to form a thin layer thereof over the free surface of saidlayer of polymer composition, the thickness of said thin layer of liquidbeing in the range of 0.1 mm to 1 cm.
 13. Process as in claim 12 inwhich the thickness of said thin layer of liquid is 1 to 5 mm and inwhich coagulating liquid is continuously supplied to said thin layerthereof.
 14. Process as in claim 12 in which the width of said gap is inthe range 0.1 to 8 mm.
 15. Process as in claim 12 in which the width ofsaid gap is in the range 2 to 7 mm.
 16. A method of making a water vaporpermeable polymer sheet material which comprises forming an initialmixture comprising elastomeric thermoplastic polyurethane dissolved indimethylformamide with microscopic water soluble inorganic saltparticles dispersed through the mixture, forming a layer at least 0.5 mmthick of the initial mixture in adherence with a support, passing thelayer in adherence with the support past a plate spaced from the freesurface of the said layer a distance such that on supplying an aqueousnon solvent liquid to The gap between the plate and the layer a meniscusis formed at the upstream end of the gap and supplying the said aqueousnon-solvent for the polymer to the said gap so as to establish andmaintain the said meniscus of non solvent at the upstream end of the gapand coagulating said layer by the action of aqueous non-solvent liquidthereon.